JPS6152041A - Optical transmission method - Google Patents

Abstract

PURPOSE:To eliminate transmission disturbance due to noise by applying FM modulation to a luminance signal and a synchronizing signal by a carrier wave including a high frequency signal, converting conversely a chrominance signal and a chrominance synchronizing signal into a signal occupying a low frequency band and applying FM modulation to a sound signal into a signal of an intermediate frequency. CONSTITUTION:A Y/C separation circuit 1 consists of low and high pass filters 2, 3 and separates a video signal into a luminance signal and a chrominance carrier wave signal. The luminance signal and the synchronizing signal from the filter 2 are modulated by an FM modulation circuit 4 by using a high frequency as a carrier wave. The chrominance carrier wave signal and the chrominance synchronizing signal from the filter 3 are subject to low frequency conversion by a low frequency conversion circuit 5. A sound signal is subject to FM modulation by FM modulation circuit 6. These signals are superimposed by a superimposing device 10 via high pass filters 7, 8, 9 and converted into an optical signal by an optical output device 11. A photoelectric converter 12 of the receiver receives an optical signal and separates the luminance signal, the sound signal and the low frequency conversion chrominance signal via extracting filters 13, 15. The separated signals are demodulated by demodulation circuits 16, 17, 19 of the next stage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical transmission method for transmitting video signals and audio signals by light, which is free from transmission interference from noise and which improves frequency characteristics in high frequencies. It is an object of the present invention to provide a new optical transmission method that does not cause deterioration and can also transmit audio signals together with video signals without any problems.

Conventional technology If video signals and audio signals are transmitted using light, it becomes possible to spatially transmit video signals and audio signals captured by a video camera to a nearby video tape recorder, etc., and a cable television method system. Coaxial cables can be replaced with optical fibers. However, if a color television signal, for example, a composite video signal of the NTSC system, is directly transmitted to the outside by light using a light emitting element, various problems arise. To explain this point according to FIGS. 6 and 7, the composite video signal consists of a luminance signal, a synchronization signal, a carrier color signal, and a color synchronization signal as shown in FIG.
As shown in the figure. And the carrier color signal is 3.58MH
However, since the light emitting diode that converts electrical signals into optical signals does not necessarily have high frequency characteristics, this may interfere with the transmission of the carrier color signal, which is carried at a high frequency of approximately 3.58 MHz. This results in the problem of high frequency deterioration.

Furthermore, since the luminance signal occupies an extremely wide band from 4.5 MHz to OHZ, there is no bandwidth available for the audio signal, making it impossible to transmit the audio signal at the same time as the video signal.

Furthermore, in the case of spatial transmission, it is adversely affected by external light. First, since the luminance signal and color difference signal of the video signal are amplitude modulated, they are directly interfered with by external light. Furthermore, low-frequency noise from fluorescent lights and the like is present indoors.

The luminance signal includes a DC signal, and the synchronization signal includes a low frequency component. Therefore, there is a problem in that the brightness signal and the synchronization signal are interfered with by low-frequency noise caused by fluorescent lamps or the like, that is, noise is added to the brightness signal and the synchronization signal.

The negative effects of external light that occur when performing spatial transmission can be avoided by transmitting a carrier wave with a very high frequency that is FM modulated with a video signal, but in such a case, the frequency band will be limited. Several - tens of MHz
Therefore, the light emitting elements that can be used are limited to special ones, leading to an increase in the cost of the device.

Problems to be Solved by the Invention The present invention attempts to solve each of the above problems.
It is an object of the present invention to provide a new optical transmission method which is free from transmission interference from noise and deterioration of frequency characteristics in high frequencies, and which can also transmit audio signals together with video signals without any problems.

Means for Solving the Problems In order to solve the above problems, the present invention employs FM modulation of a DC component, a luminance signal including a low frequency component, and a synchronization signal using a signal having a high frequency such as 4.5 MHz as a carrier wave. Conversely, color signals and color synchronization (color burst) signals with many high-frequency components are converted into signals that occupy a low frequency band centered around 688 KHz, and the audio signal is converted into m
FM modulation is performed so as to occupy a frequency band between the band occupied by the open signal and the synchronization signal and the band occupied by the color signal.

Effect Since the above means is used, according to the present invention, the synchronization signal and the luminance signal, which have many low-frequency components, are first FM-modulated using a high-frequency carrier wave, so that they are not interfered with by low-frequency noise. Furthermore, the carrier color signal and the color synchronization signal, which have many high frequency components and thus face the problem of high frequency deterioration, are converted to low frequency, thereby avoiding the problem of high frequency deterioration. As for audio signals, F
Since it is M-modulated, it is possible to transmit audio signals at the same time as video signals.

Embodiments The optical transmission method of the present invention will be explained below according to embodiments shown in the accompanying drawings.

Figures 1 to 3 are for explaining an example of the implementation of the optical transmission method of the present invention. In the figure, 1 is a Y/C two-shunt circuit that separates a composite video signal into a luminance signal and a carrier color signal, and consists of a low-pass filter 2 and a bypass filter 3. A low-pass filter 2 extracts a luminance signal and a synchronization signal, and a bypass filter 3 extracts a carrier color signal and a color synchronization signal (color burst signal). The luminance signal and synchronization signal output from the low-pass filter 2 are converted to 4.5M by the FM modulation circuit 4.
FM modulation is performed using a high frequency wave of Hz as a carrier wave fy. The carrier color signal and color synchronization signal output from the bypass filter 3 are low-pass converted into signals of 688 KHz in the low-pass conversion circuit 5. Specifically, the carrier color signal and color synchronization signal are converted to a frequency of about 3KHz, which is the frequency of the carrier color signal and color synchronization signal. .688KH than 58MHz
By adding a high frequency of z high frequency, that is, by frequency mixing, a low frequency conversion color signal of 688KH2 is obtained.

6 is an FM modulation circuit for FM modulating the audio signal; for example, 1
．． Outputs an FM-modulated audio signal using a 5 MHz high frequency as a carrier wave fa.

The FM-modulated luminance signal and synchronization signal pass through a bypass filter 7, and the low-pass converted color signal passes through a bypass filter 8.
and the above FM audio signal is applied to a superimposer 10 via a bandpass filter 9, and these three signals are superimposed. The output signal of this superimposed device 10 is then transmitted to the optical output device 1.
1 into an optical signal.

Figure 2 shows the frequency spectrum of the light signal output from the optical output device 11. The FM-modulated luminance signal (and synchronization signal) occupies a band from about 2 MHz to 5 MHz, and has a low The gamut-converted color signal occupies a band of approximately ±500 KH2 centered at 688 KHz. The FM audio signal occupies a frequency band between the luminance signal and the low frequency conversion color signal.

Figure 3 shows the circuit configuration of a receiver, which receives the optical signal output from the transmitter shown in Figure 1 and allows the signal to be reproduced on a television receiver. It is. In the figure, 12 is a photoelectric converter;
It receives a light signal from the photodetector 11 of the transmitter shown in FIG. 1 and converts it into an electrical signal. 13 to 15 are luminance signals F-modulated from the output signal of the photodetector 11;
This is a filter that separates and extracts the M-modulated audio signal and the low frequency conversion color signal. 13 is a bypass filter that passes signal components having a frequency of 2 MHz or more. ) is extracted. Reference numeral 14 denotes a low-pass filter that passes signal components having frequencies below IMHZ, and a low-pass converted color signal is extracted by this low-pass filter 14. 15 is IH
This filter 15 is a pan 1 bus filter that passes signals of Mz or more and 2 or more and 2 or more Hz or less, and the FM audio signal is extracted by this filter 15.

The luminance signal (and synchronization signal) output from the bypass filter 13 is FM demodulated by the FM demodulation circuit 16. The low-pass conversion color signal output from the low-pass filter 14 is converted by the reproduction frequency conversion circuit 17 into a carrier color signal before low-pass conversion.

The luminance signal and synchronization signal outputted from the FM demodulation circuit 16 and the carrier color signal outputted from the reproduction frequency conversion circuit 17 are superimposed by a superimposition device 18 to form a composite video output signal.

Further, the FM audio signal output from the band pass filter 15 is FM demodulated by the FM demodulation circuit 19. The video output signal outputted from the superimposing device 18 and the audio output signal outputted from the FM demodulation circuit 19 are input to a not-shown image receiving device, and the image and audio are reproduced in the image receiving device.

4 and 5 are for explaining another embodiment of the optical transmission method of the present invention.

In this embodiment, in the transmitter shown in FIG. 4, two color difference signals R-
Y, B-Y are demodulated, and the color difference signals R-Y, B-Y are F
The M demodulation circuit z1.22 generates a carrier wave (f
cl, fc2) for FM modulation. Carrier frequency fcL
, fc2 belong to a lower band than the FM-modulated audio signal, and are selected so as to satisfy the condition that the bands of the two color difference signals R-Y and B-Y do not overlap. That is, fcl
Suitably higher than 688KHz, and set fc2 to fcl and 6
88K) (The frequency is set lower than 688KHz by the difference from z.The processing for the luminance signal and audio signal in the transmitter is the same as in the first embodiment.

In the receiver shown in FIG.
．． FM demodulation is performed at 24. The FM demodulated color difference signals R-Y and B-Y are input to the color encoder 25 together with the FM demodulated luminance signal in the FM demodulation circuit 16.
It is considered to be a composite video output signal. This video output signal and the audio signal subjected to FM modulation in the FM demodulation circuit 19 are input to an image receiving device (not shown), and the image and audio are reproduced in the image receiving device.

According to the optical transmission method of each of the above embodiments, the synchronization signal and the luminance signal are transmitted using a carrier wave with a high frequency of, for example, 4.5 MHz.
Since it is M-modulated and optically transmitted, it is not affected by low-frequency noise at all.Also, the general color feeding signal and color synchronization signal are converted into signals that occupy the low frequency range and then optically transmitted, so there is no problem with high frequency degradation. The problem can be avoided. As for the audio signal, the frequency of the carrier wave is selected and FM modulated so as to occupy the frequency band between the band occupied by the synchronization signal and the luminance signal and the band occupied by the carrier color signal and color synchronization signal.
It becomes possible to transmit audio signals together with video signals, which conventionally could not be transmitted together with video signals.

Note that the frequency of the carrier wave for carrying the color signal (color synchronization signal) is 1±688 KHz in the first embodiment, and the frequency of the carrier wave for the luminance signal and synchronization signal is 4.5 MHz in each embodiment. Although the carrier wave for the audio signal was 1.5 MH2, this is just one embodiment, and the present invention is not limited to this.As described above, the present invention The optical transmission method converts the chrominance signal of the composite video signal into a signal occupying a lower frequency band, and converts the synchronization signal and luminance signal of the composite video signal into a frequency higher than the frequency band occupied by the chrominance signal. FM modulating the audio signal so as to occupy a frequency band, and FM modulating the audio signal so as to occupy a frequency band between the occupied band of the color signal and the occupied band of the synchronization signal and the luminance signal.
It is characterized in that these signals are modulated and then superimposed on each other, and the signal obtained by the superposition is converted into an optical signal. Therefore, according to the optical transmission method of the present invention, the chrominance signal is converted into an optical signal after being converted to a low frequency band so that it occupies a low frequency band, so there is a problem of high frequency deterioration, and the chrominance signal is susceptible to interference due to high frequency noise. You can avoid the problem of receiving it. Furthermore, since the brightness signal and the synchronization signal are FM-modulated so as to occupy a high frequency band, the problem of the brightness signal and the synchronization signal being disturbed by low frequency noise can also be avoided. Since the audio signal is FM modulated to occupy the frequency band between the band occupied by the color signal and the band occupied by the luminance signal and synchronization signal, it is possible to transmit the audio signal by light at the same time as the video signal. It becomes possible.

[Brief explanation of the drawing]

1 to 3 are for explaining an example of implementation of the optical transmission method of the present invention. FIG. 1 is a circuit block diagram showing the circuit configuration of the transmitter, and FIG. 2 is a circuit block diagram showing the circuit configuration of the transmitter. A frequency spectrum diagram, FIG. 3 is a circuit block diagram showing the circuit configuration of the receiver, FIGS. 4 and 5 are for explaining other embodiments of the optical transmission method of the present invention, and FIG. Figure 5 is a block diagram showing the circuit configuration of the receiver, Figure 6 is a waveform diagram of the composite video signal, and Figure 7 is a frequency spectrum diagram of the composite video signal. It is. Explanation of symbols 4... FM modulation circuit that modulates the fist luminance signal and synchronization signal, 5.21.22... Circuit that converts the tone signal into a signal occupying a low frequency band, 6... FM modulates the audio signal FM modulation circuit that modulates, 1
0...Circuit for superimposing signals, 11...Means for converting signals into optical signals Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Claims] (1) Converting the color signal of the composite video signal into a signal that occupies a lower frequency band, and converting the synchronization signal and luminance signal of the composite video signal into a higher frequency band that is separated from the band occupied by the color signal. The audio signal is FM modulated so as to occupy a frequency band between the chrominance signal's occupied band and the synchronization signal and luminance signal's occupied band, and these signals are then mutually An optical transmission method characterized by superimposing the signal and converting the signal obtained by the superimposition into an optical signal.